(a) Field of the Invention
The present invention relates to a sealed package of raw meat or fish which is capable of maintaining a reddish color, i.e., an indication of the freshness of raw meat or fish, and of inhibiting the oxidation and spoilage of raw meat or fish, and to a method of preserving raw meat or fish without losing the freshness thereof.
(b) Description of the Prior Art
A so-called "red meat or fish" presents a scarlet color while fresh, but turns, for example, brown as the freshness is lost. The red color of the meat or fish while fresh is due to myoglobin or hemoglobin, myoglobin generally occupying 80 to 90%. Myoglobin present in the meat is combined with oxygen in the air to form oxymyoglobin. If oxymyoglobin is oxidized to metmyoglobin, the meat turns brown.
The meat packed in the conventional method is readily exposed to the oxygen in the air during transportation, resulting in change or fading of the meat's color, oxidation of the lipid portion and spoilage of the meat, thereby shortening the storage life thereof. For example, chilled beef is generally packed with a shrinkable film of EVA/PVDC/EVA. In this case, the packed beef is exposed to the oxygen remaining in the package or permeating through the film, resulting in change or fading of the meat's color, oxidation of its lipid portion and spoilage of the packed beef.
To overcome the above-noted defect, a method of preserving raw meat is provided in which the raw meat is packed with a gas-impermeable material and a deoxidant is sealed in the package. The conventional method of preserving raw meat utilizing a deoxidant is disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 51-104061, Japanese Patent Publication (Kokoku) No. 54-34822, Japanese Patent Disclosure (Kokai) No. 58-158129, Japanese Patent Disclosure (Kokai) No. 58-183033, and Japanese Patent Disclosure (Kokai) No. 54-41355. In the prior art of this type, myoglobin, i.e., the red component of raw meat, remains in its reduced state by the deoxidation effect. When the package is unsealed, the raw meat is exposed to the oxygen in the air, with the result that the reddish purple of the reduced myoglobin is changed into scarlet of the oxidized myoglobin.
What should be noted is that it is unavoidable for the raw meat to be turned reddish purple or reddish black even in the absence of oxygen. Specifically, the metmyoglobin, which displays a brown color, in the raw meat after the deoxidation is reduced to reduced myoglobin, which displays a reddish purple color, under the action of a metmyoglobin reduction enzyme. It follows that the raw meat packed together with the deoxidant is kept reddish purple because of the presence of the reduced myoglobin in the package.
Japanese Patent Disclosure 54-41355 referred to previously teaches the use of a deoxidant which generates carbon dioxide gas. In this case, freshness of the raw meat under preservation is maintained by the bacteriostatic effect of the carbon dioxide gas. However, the deoxidant used in this prior art generates carbon dioxide gas after the oxygen within the package has been absorbed, not immediately after initiation of the oxygen absorption. It follows that, if the CO.sub.2 -generating type deoxidant is used for preservation of raw meat, oxygen is selectively absorbed in the initial stage, resulting in a low oxygen concentration within the package and, thus, in a change of color of the raw meat to brown. It should be noted that, even if the raw meat whose color has been turned brown is exposed to carbon dioxide gas, it is impossible to restore the original scarlet color of the raw meat.